Hydrophone drogue

ABSTRACT

A non-fouling, high drag, packageable drogue for substantially reducing the current flow past a suspended hydrophone. A single rectangular sheet capable of high density packaging in a sonobuoy cannister is selectively sized to provide the desired drag area. Upon deployment the drogue is held in an open widthwise position by upper and lower resilient spreaders and in an open lengthwise position by the weight of the hydrophone thereby obviating possible collapse or fouling as the relative current flow diminishes.

United States Patent 11 1 1111 3,922,989 McEachern 1 Dec. 2, 1975 HYDROPHONE DROGUE 3,711,821 1/1973 Dale et 9/8 R x [75] Inventor: James F. McEachern, Hatboro, Pa.

Primary ExaminerGeorge E. A. l-lalvosa i 1 Asslgneei The United States of America as Assistant Examiner-Stuart M. Goldstein represented y the Secretary of the Attorney, Agent, or FirmR. S. Sciascia; Henry Navy, Washington, DC. Hansen [22] Filed: Nov. 4, 1974 21 Appl. No.: 520,703 {57] ABSTRACT A non-fouling, high drag, packageable drogue for sub- U S 114/209 stantially reducing the current flow past a suspended [51] In.t.Cl; 21/48 hydrophone A Single rectangular Sheet Capable of 58 Field of Search 114/209; 9/8 R; 340/2, f l gackagmgdm a Z P Q W 340/3 T R 5 R ectlve y s1ze to provi et e eslre rag area. pon deployment the drogue 1s held in an open w1dthw1se position by upper and lower resilient Spreaders and in [56] References Cited an open lengthwise position by the weight of the hy- UNITED STATES PATENTS drophone thereby obviating possible collapse or foul- 378,l7l 2/1888 McCarthy 114/209 ing as the relative current flow diminishes. 1,012,890 12/1911 Miller r 2785.646 3/1957 Meyer 114/209 2 Clalms, 7 Drawmg Flgures US. Patent Dec. 2, 1975 I I 3,922,989 Q HYDROPHONE DROGUE STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates generally to drag devices used in hydrophone suspension systems and particularly to a high drag drogue which is formed from a single sheet of material and which is easily packaged in a conventional sonobuoy cannister.

Typical ocean current speed profiles indicate that current velocities are greatest on the ocean surface and decrease proportionally with increasing depth. In a sonobuoy suspension system having a float at the ocean surface and a hydrophone at the end of a suspension cable, the relatively large velocity component at the ocean surface creates a drag force on the surface float which tends to pull the hydrophone through the subsurface water thus generating spurious signals due to the high relative current flow. By placing a drag device in the suspension system in the vicinity of the hydrophone the relative current flow past the hydrophone can be reduced and, if a large enough area can be exposed to the current flow, the hydrophone can be virtually locked to the flow and the relative current would approach zero. Known drogue designs have utilized drag devices consisting of inflated cylindrical shapes which provide adequate virtual mass for surface wave isolation but present drag areas of less than two square feet. The complicated design and the limited packaging space in sonobuoy cannisters precludes simply expanding the size of these devices to achieve the desired drag area. Parachute style drag devices have been used and are able tosupply the necessary amount of drag and meet packaging requirements. Such devices, however, are subject to unreliable deployment and are prone to fouling in the buoy suspension and interfering with the hydrophone sensor.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a high drag sonobuoy drogue which will reduce relative current flow past a suspended hydrophone to desirable levels. Another object of the invention is to provide an easily packageable drogue which can be readily contained within conventionally sized sonobuoy cannisters. Yet another object of the present invention is to provide a sonobuoy drogue which will neither foul nor collapse during deployment or operation.

Briefly, these and other objects are accomplished by a non-fouling, packageable, high drag drogue having a single sheet of flexible material capable of high density packaging and which is selectively sized to provide the desired drag area. Upon deployment the sheet isheld in an open widthwise position by upper and lower resilient spreaders. The drogue is held in the open lengthwise position by the weight of the hydrophone thus obviating possible collapse or fouling as the relative current speed diminishes.

For a better understanding of these and other aspects of the invention, reference may be made to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a deployed sonobuoy system utilizing the drogue of the invention;

FIG. 2 is a broadside view of the deployed drogue in accord with the invention;

FIGS. 3A-3D illustrate the folding sequence of the drogue for packing into a cannister, and FIG. 4 is a sectional view of a cannister having packed therein the folded drogue of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is shown a deployed sonobuoy system 10 having a float 12 floating on the top surface of a water body such as an ocean. Attached to the float 12 at one end is a primary suspension cable 14 having its other end connected to the upper portion of a drogue 16. The lower portion of the drogue 16 is connected to one end of a secondary suspension cable 18 whose other end is connected to and supports a hydrophone 20. In conventional sonobuoy systems the primary suspension cable 14 will be of a length much greater than that of the secondary suspension cable 18 with the intended result that the drogue 16 is placed as close as possible to the hydrophone 20 and thus substantially locks the movement of the hydrophone 20 to that of the drogue 16 which in turn is positioned according to subsurface current flow.

Referring now to FIG. 2 there is shown a magnified view of the drogue 16 as noted in FIG. 1. The drogue 16 has as its main body a single elongated sheet 22 formed from a light weight water-impervious material such as, for example, polyethelene. The sheet 22 is shaped to be symmetrical along its longitudinal axis and may be, for example, a rectangle as shown. In its deployed position the sheet 22 is held in an open position widthwise by an upper spreader 24 and a lower spreader 26. The spreaders 24, 26 are attached respectively to the upper and lower ends of the sheet 22 in any convenient manner such as, for example, thermally fusing the spreader within folded ends of the sheet 22. The spreaders are made of any conventional resilient material such as, for example, spring steel which will allow folding the spreader upon itself while at the same time retaining enough force to spring to its nondeformed state while within a water body. The spreaders are preconditioned to spread out in a relatively straight line when used in the deployed state. Additional stability may be imported to the drogue by preconditioning the spreaders to provide a minor arcuate contour as shown in FIG. 1 which, upon deployment, insures that the drogue always provides either a convergent or divergent broadside surface to the flow of water. Attached to the upper corners of the sheet 22 and in common arrangement with the respective ends of the upper spreader 24 is an upper harness 28 formed of two equal lengths of waterproof cord such as, for example, nylon or polyethelene. Each of the cord lengths within the harness 28 are connected at one end respectively to the upper comers of the sheet 22 and at their other ends are connected in common to an upper support ring 30. Similarly, there is provided a lower harness 32 having two equal lengths of cord which are each connected at one end respectively to the lower corners of the sheet 22 and at their other ends are connected in common to a lower support ring 34. The harnesses 28, 32 may be attached to the sheet 22, for example, by passing the respective cord ends through the sheet thus looping the spreader for extra strength or by passing the cord ends through common holes in both the sheet and the spreaders. As earlier noted in FIG. 1, the upper support ring 30 is attached in any convenient manner to the lower end of the primary suspension cable 14 and the lower support ring 34 is attached in any convenient manner to the secondary suspension cable 18 or, in some situations, may be directly attached to the hydrophone 20 or other similar terminal mass. The drogue 16 is held in its deployed position lengthwise by the weight of the hydrophone 20 or other terminal mass and the upward supporting force of the float 12. The opposing forces of the float 12 and the hydrophone 20 are thus independent of the relative current flow and prevent the possible collapse or fouling of the drogue should the relative current diminish or disappear.

It has been ascertained that the flow of subsurface ocean water past a hydrophone sensor and which is designated as relative current should desirably be maintained at less than or equal to 0.10 knots for an A size sonobuoy cannister which measures approximately 4% inches diameter by 36 inches in length. Ideally, of course, the sonobuoy should be locked to the current flow thus eliminating practically all spurious input signals due to the relative current and which would then be operating under a condition of near zero relative current flow. In order to maintain the relative current to less than or equal to 0.10 knots in an A size sonobuoy system, the drogue should have a drag area of no less than square feet.

Accordingly, the polyethelene sheet 22 shown in FIG. 2 is sized by way of example to have a width of approximately 2.0 feet and a height of approximately 7.5 feet. Also, the thickness of the sheet 22, for example, is 0.012 inches thus providing a realistic median between packaging density and strength. Obviously, other dimensions and thicknesses of the sheet 22 may be utilized to achieve the objects of the present invention. The length, or height, of the sheet, however, is desirably greater than or equal to the width in order to preserve drogue stability.

Referring now to FIGS. 3A3D, there is shown a folding sequence for packing the drogue 16 into a cannister. Upon depolyment the unfurling of the drogue occurs in a sequence reverse to that shown in FIGS. 3A-3D. FIG. 3A illustrates the drogue 16 in its unfurled or deployed position. Referring now to FIG. 3B, the first step in folding the drogue 16 is to fold it over itself lengthwise with a single fold being at the midpoint between the ends of the sheet attached to the respective support rings. During this and succeeding portions of the folding sequence the upper and lower support rings should be maintained separate from one another so as to avoid any possible fouling. The second step of before-mentioned A" size container. The drogue is easily unfurled beginning with the reverse ofthe second folding step shown in FIG. 3C and may be packed into a suitably sized cannister at this point. The upper support ring and its attached upper harness is placed in an upward direction and the lower support ring with its attached lower harness is placed in an opposing direction to that of the upper harness. The entire furled drogue as shown in FIG. 4 is then packed within the applicable sonobuoy cannister 15 with the upper support ring attached to an primary suspension cable and the lower support ring attached to the secondary suspension cable of hydrophone.

Thus it may be seen that there has been provided a novel high drag drogue device which is easily packageable within conventional sonobuoy canisters and which is neither fouling nor collapsible in its deployed position.

Obviously many modifications and variations of the invention are possible in light of the above teachings. For example, conventional vertical mass devices such as discs or containers to entrain water can be used in tandem with the drogue of the invention. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A non-fouling deployable sonobuoy drogue system suitable for placement in a cannister, comprising, in combination:

a hydrophone;

a flexible rectangular sheet having two linear springs contiguously attached along their lengths to respective ones of opposed edges of said sheet;

said sheet being folded in half between said opposed edges to form an intermediate edge with said springs coinciding with each other, and being furled about said intermediate edge to form an elongated spiral roll with the opposed edges exposed and operatively connected to said float and said hydrophone, respectively; and

said roll being folded in half along its length against the force of said springs to form distal sides slidably receivable within the cannister;

whereby said roll unfolds under the force of said springs when deployed from the cannister, and then unfurls under tension of said hydrophone.

2. A non-fouling unfurlable drogue suitable for deployment by a weight from one end of a flotation cannister. comprising:

a flexible rectangular sheet having two linear springs contiguously attached along their lengths to respective ones of opposed edges of said sheet;

said sheet being folded in half between said opposed edges to form an intermediate edge with said springs coinciding with each other, and being furled about said intermediate edge to form an elongated spiral roll with the opposed edges exposed for operative connection to the flotation cannister and the weight, respectively; and

said roll being folded in half along its length against the force of said springs to form distal sides slidably receivable within the cannister;

whereby said roll unfolds under the force of said springs when deployed from the cannister, and

then unfurls under tension of the weight. 

1. A non-fouling deployable sonobuoy drogue system suitable for placement in a cannister, comprising, in combination: a float; a hydrophone; a flexible rectangular sheet having two linear springs contiguously attached along their lengths to respective ones of opposed edges of said sheet; said sheet being folded in half between said opposed edges to form an intermediate edge with said springs coinciding with each other, and being furled about said intermediate edge to form an elongated spiral roll with the opposed edges exposed and operatively connected to said float and said hydrophone, respectively; and said roll being folded in half along its length against the force of said springs to form distal sides slidably receivable within the cannister; whereby said roll unfolds under the force of said springs when deployed from the cannister, and then unfurls under tension of said hydrophone.
 2. A non-fouling unfurlable drogue suitable for deployment by a weight from one end of a flotation cannister, comprising: a flexible rectangular sheet having two linear springs contiguously attached along their lengths to respective ones of opposed edges of said sheet; said sheet being folded in half between said opposed edges to form an intermediate edge with said springs coinciding with each other, and being furled about said intermediate edge to form an elongated spiral roll with the opposed edges exposed for operative connection to the flotation cannister and the weight, respectively; and said roll being folded in half along its length against the force of said springs to form distal sides slidably receivable within the cannister; whereby said roll unfolds under the force of said springs when deployed from the cannister, and then unfurls under tension of the weight. 